-LRB- CNN -RRB- -- Sinn Fein leader Gerry Adams was released Sunday after four days in police custody in connection with the 1972 abduction and killing of a mother of 10 by the Irish Republican Army , police in Northern Ireland said .

Adams , 65 , has long denied having any role in the death of Jean McConville , a widow who was reportedly killed by the IRA four decades ago because the group believed she was a spy for the British army .

Adams is a prominent Catholic politician who helped broker peace in Northern Ireland and who has long been associated with the IRA , once considered the armed wing of Sinn Fein . Today , Sinn Fein is Ireland 's second-largest opposition party .

`` Let me be very clear : I am innocent of any involvement in any conspiracy to abduct , kill or bury Mrs. McConville , '' Adams said soon after his release .

He told reporters he bears no animosity toward anyone and spoke about the need to move forward .

`` I 'm an activist . This is my life , and I 'm philosophical , and I understand that I have detractors and opponents -- and I especially understand that there -LSB- are -RSB- sinister elements who are against the changes Sinn Fein and others are committed to achieving , '' Adams said .

He added : `` There 's only way for our society to go -- and that 's forward . ''

Adams had surrendered himself for questioning Wednesday evening and his detention had threatened the fragile peace in Northern Ireland , a peace Adams is in part credited with bringing about after decades of sectarian tensions .

The questioning of Adams was not unexpected . Adams said he told authorities last month that he was willing to meet with investigators .

Martin McGuinness , deputy first minister of Northern Ireland , said last week in Belfast that Adams ' arrest was unnecessary , unjustified and politically motivated .

He said that he had seen the `` dark side '' of Northern Ireland policing `` flex its muscles in the course of the past couple of days '' and that the arrest was a '' ` deliberate attempt to influence the elections that are due to take place in three weeks ' time . ''

A number of other people have been arrested and questioned in the investigation into McConville 's abduction and killing .

One man has been charged with aiding and abetting the crime . He denies wrongdoing .

The IRA admitted in 1999 to killing a number of people who have become known as `` The Disappeared , '' those who vanished during the so-called Troubles , a 30-year conflict between Protestant loyalists who wanted to stay part of the United Kingdom and Catholic nationalists who wanted to see the north united with Ireland .

Among the victims was McConville , 37 , whose remains were found partially buried on a beach in County Louth in 2003 . She died of a single gunshot wound to the back of the head .

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NEW : `` There 's only way for our society to go -- and that 's forward , '' says Adams

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The Sinn Fein leader says he was n't involved in a 1972 killing

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Adams is now a prominent politician who helped broker peace in Northern Ireland

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One other politician said the arrest was an attempt to influence an election